1. Field of the Invention
This invention relates to alignment of optical devices. More particularly this invention relates to apparatus and method for the automatic optical alignment of two linear structures.
2. Description of the Related Art
In the past, the assembly and manufacture of optical assemblies having a linear array of optical elements has been time consuming and prone to quality control problems. The latest developments in optical cross-connect assemblies have only magnified these problems. Precisely engineered optical receiver arrays are required in these assemblies. A general demand for more precisely constructed assemblies having greater reliability has translated into a demand for better manufacturing apparatus and processes.
Optical devices of the type addressed by the present invention currently in use involve an array of optical fibers having light transmitted therethrough. The light exiting the end faces of the fibers is transmitted through a plurality of waveguides, which produce a diffraction pattern. The diffracted light is collimated by focusing optics, and then falls on a detector array.
In order to equalize the signals falling on individual elements of the detector array, it is necessary that the detector array be precisely aligned with respect to the axis of the waveguides and the focusing optics. Optimizing the alignment has heretofore been a tedious, labor intensive process. In some applications the detector array is positioned manually, and adjustment of the input elements is performed using a manual technique. This is because the cross section of the detectors is large enough to permit manual manipulation.
It is therefore a primary object of some aspects of the present invention to improve the manufacture of optical linear arrangements.
It is another object of some aspects of the present invention to automate the alignment of two linear optical arrangements relative to one another with a high degree of precision.
There is thus provided in accordance with a preferred embodiment of the invention a method of alignment, which includes the steps of:
holding a first optical element in opposition to a second optical element for interalignment therewith, the second optical element including a plurality of receivers including a first marginal receiver and a second marginal receiver, the first optical element having a first axis and a second axis, and the second optical element having a third axis and a fourth axis,
detecting a plurality of light signals that pass from the first optical element to the second optical element, the light signals including a first light signal that impinges on the first marginal receiver, and a second light signal that impinges on the second marginal receiver,
in a first phase of operation the first optical element is rotated about a Y-axis until the second axis is in a parallel alignment with the fourth axis and in a second phase of operation the first optical element is displaced along the Y-axis and
while displacing the first optical element along the Y-axis, recording a signal strength of one of the first light signal and the second light signal and displacing the first optical element along a Z-axis until the signal strength has an optimal value.
There is also provided in accordance with a preferred embodiment of the present invention a computer software product, which includes a computer-readable medium in which program instructions are stored and the program instructions are read by a computer, wherein the computer is connected to an alignment apparatus. The alignment apparatus includes a chuck holding a first optical element thereon, the first optical element opposing a second optical element for interalignment therewith, the second optical element includes a plurality of receivers, which includes a first marginal receiver and a second marginal receiver, the first optical element having a first axis and a second axis, the second optical element having a third axis and a fourth axis, a plurality of detectors, each of the detectors detecting light emitted from the first optical element that impinges on one of the receivers, the detectors include a first detector that detects the light impinging on the first marginal receiver, and a second detector that detects the light impinging on the second marginal receiver, a first actuator for displacing the chuck on a Y-axis, the first actuator being driven by a first motor, a second actuator for displacing the chuck on a Z-axis, the second actuator being driven by a second motor, a third actuator for rotating the chuck about the Y-axis, the third actuator being driven by a third motor, wherein the computer receives a plurality of signals from the detectors, the signals including a first signal from the first detector, a second signal from the second detector, the computer transmitting control signals to energize the first motor, the second motor, and the third motor and the instructions, when read by the computer, causes the computer to perform the steps of: in a first phase of operation, energizing the third motor to rotate the chuck about the Y-axis until the second axis is in a parallel alignment with the fourth axis and in a second phase of operation energizing the first motor to displace the chuck along the Y-axis, while performing the step of energizing the first motor, recording a response of one of the first detector, the second detector and energizing the second motor to displace the chuck along the Z-axis until a first function of the response has an optimal value.
There is further provided in accordance with a preferred embodiment of the present invention an alignment apparatus, which includes a chuck holding a first optical element thereon, the first optical element opposing a second optical element for interalignment therewith, the second optical element including a plurality of receivers including a first marginal receiver and a second marginal receiver, the first optical element having a first axis, the second optical element having a second axis, a plurality of detectors, each of the detectors detecting light emitted from the first optical element that impinges on one of the receivers, the detectors include a first detector that detects the light impinging on the first marginal receiver, and a second detector that detects the light impinging on the second marginal receiver, a first actuator for displacing the chuck on a Y-axis, the first actuator being driven by a first motor, a second actuator for displacing the chuck on a Z-axis, the second actuator being driven by a second motor, a third actuator for rotating the chuck about the Y-axis, the third actuator being driven by a third motor, a computer, receiving a plurality of signals from the detectors, the signals including a first signal from the first detector, a second signal from the second detector, the computer transmitting control signals to energize the first motor, the second motor, and the third motor, computer program instructions being stored in the computer, which instructions. When the instructions are read by the computer, the computer performs the steps of: in a first phase of operation energizing the third motor to rotate the chuck about the Y-axis until the first axis is in a parallel alignment with the second axis and in a second phase of operation energizing the first motor to displace the chuck along the Y-axis. While performing the step of energizing the first motor, recording a response of one of the first detector, the second detector and energizing the second motor to displace the chuck along the Z-axis until a first function of the response has an optimal value.
There is further provided in accordance with yet another preferred embodiment of the present invention an alignment apparatus, which includes a chuck holding a first optical element thereon, the first optical element opposing a second optical element for interalignment therewith, the second optical element being carried on a substrate, the second optical element including a plurality of receivers including a first marginal receiver and a second marginal receiver, the first optical element having a first axis and a second axis, the second optical element having a third axis and a fourth axis, a first actuator for displacing the chuck on a Y-axis, the first actuator being driven by a first motor, a second actuator for displacing the chuck on a Z-axis, the second actuator being driven by a second motor, a third actuator for rotating the chuck about the Y-axis, the third actuator being driven by a third motor, a fourth actuator for rotating the chuck about the Z-axis, the fourth actuator being driven by a fourth motor, a third optical element, directing a beam along the Z-axis in a light path that extends between a light source and the second optical element via the first optical element, a plurality of detectors, each of the detectors detecting the beam impinging on one of the receivers, the detectors including a first detector that detects the beam impinging on the first marginal receiver, and a second detector that detects the beam impinging on the second marginal receiver, a computer, receiving a plurality of signals from the detectors, the signals including a first signal from the first detector, a second signal from the second detector, the computer transmitting control signals to energize the first motor, the second motor, the third motor, and the fourth motor, computer program instructions being stored in the computer, which instructions, when read by the computer. The computer performs the steps of: in a first phase of operation energizing the third motor to rotate the chuck about the Y-axis until the second axis is in parallel alignment with the fourth axis, in a second phase of operation energizing the first motor to displace the chuck along the Y-axis, while performing the step of energizing the first motor, recording a response of one of the first detector, the second detector and energizing the second motor to displace the chuck along the Z-axis until a first function of the response has an optimal value and in a third phase of operation energizing the fourth motor to rotate the chuck about the Z-axis until the first signal and the second signal are equalized.
Further in accordance with a preferred embodiment of the present invention the first axis and the third axis are substantially parallel and second and the fourth axis are substantially parallel.
Still further in accordance with a preferred embodiment of the present invention the first axis and the second axis are substantially orthogonal and the third axis and the fourth axis are substantially orthogonal.
Further in accordance with a preferred embodiment of the present invention the step of recording the signal strength further includes the step of determining a full-width half maximum (FWHM) of the signal strength.
Additionally in accordance with a preferred embodiment of the present invention the step of recording the signal strength further includes determining a full-width half maximum squared of the signal strength, wherein the optimal value is a minimum value of the full-width half maximum squared.
Further in accordance with a preferred embodiment of the present invention the method also includes the steps of:
displacing the first optical element stepwise on an interval of the Z-axis, defining a plurality of incremental positions thereon, in the first phase of operation, such that at each of the incremental positions displacing the first optical element on an interval of the Y-axis,
while displacing the first optical element on the interval of the Y-axis is being performed, determining a function of the first light signal and determining the function of the second light signal,
after the step of displacing the first optical element stepwise on the interval of the Z-axis has been performed, determining a first point on the Z-axis where the function of the first light signal has a first optimum value and a second point on the Z-axis where the function of the second light signal has a second optimum value, calculating a difference xcex94Z between the second point and the first point, responsive to the step of calculating rotating the first optical element about the Y-axis to reduce a distance between the first marginal receiver and the second point.
Preferably, the step of rotating the first optical element about the Y-axis includes rotation by an angle xcex8 that is given by
xcex8=sinxe2x88x921(xcex94Z/d)
where d is a displacement between the first marginal receiver and the second marginal receiver.
Further in accordance with a preferred embodiment of the present invention the function is a full-width half maximum, the first optimum value and the second optimum value are each a minimum value of the function.
Additionally in accordance with a preferred embodiment of the present invention the method further includes the steps of, in the second phase of operation:
in a first iteration displacing the first optical element on an interval of the Y-axis,
while the step of displacing the first optical element is being performed in the first iteration, determining a function of at least one of the light signals to define a first determination of the function,
displacing the first optical element on the Z-axis by a first increment;
in a second iteration, displacing the first optical element on the interval of the Y-axis;
while the step of displacing the first optical element is being performed in the second iteration, determining the function to define a second determination of the function; and responsive to a difference between the first determination and the second determination, displacing the first optical element on the Z-axis by a second increment.
Further in accordance with a preferred embodiment of the present invention the function is a full-width half maximum squared.
Still further in accordance with a preferred embodiment of the present invention the step of determining the function includes determining a sum of the function of a first one of the light signals and the function of a second one of the light signals.
Further in accordance with a preferred embodiment of the present invention the method also includes the steps of:
in a first iteration: displacing the first optical element on an interval of the Y-axis,
while the step of displacing the first optical element is being performed in the first iteration, determining a first point on the Y-axis wherein a first signal has a first maximum magnitude, and determining a first magnitude of a second signal at the first point,
rotating the first optical element about the Z-axis by a first increment,
in a second iteration: displacing the first optical element on the interval of the Y-axis, while the step of displacing the first optical element is being performed in the second iteration, determining a second point on the Y-axis wherein the first light signal has a second maximum magnitude, and determining a second magnitude of the second light signal at the second point,
responsive to a difference between the first magnitude and the second magnitude, rotating the first optical element about the Z-axis by a second increment.
Further in accordance with a preferred embodiment of the present invention the computer software product the first function includes a function of a full-width half maximum of a plot of the response.
Preferably, the first function is a full-width half maximum squared, and the optimal value is a minimum value.
Additionally in accordance with a preferred embodiment of the present invention the second function is a full-width half maximum, the first optimum value and the second optimum value are each a minimum value of the second function.